Methods and systems for purifying gases

ABSTRACT

The present invention relates to methods and systems for purifying gases, such as for example semiconductor process gases. The invention more particularly relates to fluid purification methods and systems having improved heat transfer capabilities and controls such that the purified fluid produced from the process contains reduced impurity levels and/or exhibits more uniform concentrations within the final product. In another aspect of the invention, the activation time for adsorbent beds used in such processes and systems can be reduced.

FIELD OF THE INVENTION

The present invention relates generally to methods and systems forpurifying gases, such as for example semiconductor process gases. Theinvention more particularly relates to gas purification methods andsystems having improved heat transfer capabilities and controls suchthat the purified gas produced from the process contains reducedimpurity levels and/or exhibits less variability in impurityconcentration.

BACKGROUND OF THE INVENTION

Process gases such as those gases used for semiconductor processes(e.g., arsine (AsH₃), phosphine (PH₃) and ammonia (NH₃)) typically mustbe purified prior to use in semiconductor processes in order to removeimpurities (e.g., moisture, CO₂ and SO₂) to acceptable levels. Forexample, ammonia is used as a source gas in the chemical vapordeposition (CVD) of nitride films during the fabrication ofsemiconductor chips. Typical nitrides are silicon nitride, made forexample by the reaction of silane and ammonia and titanium nitride, madefor example by the reaction of titanium tetrachloride and ammonia. Thepresence of one to three thousand parts per billion (ppb) levels ofmoisture can result in a decrease of the performance properties of thenitride layer. Gallium nitride CVD technology has been shown to requireeven lower levels of moisture in the source of ammonia than silicon andtitanium nitride technology.

Purification of such gases either prior to use in semiconductorapplications or in purification after use and before re-use currentlyincludes passing the process gas through one or more beds formed of anadsorbent to remove such target impurities.

U.S. Pat. No. 6,576,138 B2 to Sateria et al. discloses a method forproducing purified semiconductor gases from its impure form usingadsorption and evaporation techniques.

U.S. Pat. No. 6,749,819 B2 relates to a process for purifying ammonia.The process relates to contacting crude ammonia with catalyst to removeoxygen and/or carbon dioxide that are present in the ammonia asimpurities. The reference also relates to contacting crude ammonia witha catalyst that contains manganese oxide as an ingredient and thencontacting the ammonia with a synthetic zeolite to remove at least oneof carbon dioxide, oxygen and moisture from the ammonia.

Adsorption processes can be sensitive to temperature. Generally, higheroperating and/or ambient temperatures will reduce adsorption efficiency.In addition, gas purification systems are often located in geographicalareas where the ambient temperature is not controlled or monitored,and/or can fluctuate significantly based on prevailing weather and otherenvironmental conditions. Consequently, there can be significantvariability in the temperature of the adsorbent bed. The adsorptionprocess itself moreover results in an increase in the temperature of theadsorbent bed, especially in cases where the moisture content of thefeed material is high. These factors can cause the quality of thematerial being purified to fluctuate on the basis of the operatingtemperature of the adsorbent bed and/or surrounding conditions.

Another factor to be considered with regard to the purification of suchgases includes the time required for activation of the adsorbent bed(s).The activation process involves heating the adsorbent bed(s) to elevatedtemperatures (for example, 100° C. to 400° C.) while flowing a dry purgegas through the bed(s). Because many adsorbents used in purificationsystems for semiconductor gases are of low thermal conductivity, it canbe difficult to control the temperature of the adsorbent bed not onlyduring purification operations, but also during the activation phase ofthe adsorbent bed.

Previous attempts to address heat transfer issues have involved severalapproaches. For example, the use of monoliths of carbon with higherthermal conductivity than granular adsorbents as the adsorbent media inthe bed to improve heat transfer is proposed in Menard, et al.,“Activated Carbon Monolith of High Thermal Conductivity for AdsorptionProcesses Improvement Part A: Adsorption Step”, Chemical Engineering andProcesses, 44 (2005), 1029-1038.

A method for heat transfer in the bed in which a finned inner-tube isenclosed in a larger tube and the adsorbent material is contained in theannulus thus formed between the two tubes is contemplated in Bonjour, etal., “Temperature Swing Adsorption Process with Indirect Cooling andHeating”, Ind. Eng. Chem. Res. 2002, 41, pages 5802-5811.

Some general means of removing moisture from fluids is discussed inWeiner, “Dynamic Fluid Drying”, Chemical Engineering, Sep. 16, 1974,pages, 92-101.

U.S. Pat. No. 4,165,972 to Iles et al. proposes heating and cooling ofthe sorbent beds by flowing coolant through the beds.

U.S. Pat. No. 5,169,413 to Leavitt relates to a pressure swingadsorption (PSA) system which includes means for controlled retention ofinternally generated, self-refrigeration such that the averagetemperature of the bed is to be reduced.

U.S. Pat. No. 5,268,022 to Garret et al. proposes a method for heattransfer within a bed that involves having at least one heat conductivemember containing a liquid medium arranged within the bed such that inoperation, heat is said to be conducted by convection through the liquidfrom a region of maximum temperature at or near the bottom of the bed toa region of minimum temperature at or near the top of the bed.

There remains a need in the art of gas purification for improvedtemperature control of adsorbent beds such that the purified gasproduced from such processes contain reduced impurity levels and/orexhibit less variability in impurity concentration. There also remains aneed to reduce the time required to activate adsorbent beds prior to useand/or reuse in such purification processes.

SUMMARY OF THE INVENTION

The present invention relates to methods and systems for purifyinggases, such as for example semiconductor process gases. Morespecifically, the invention provides gas purification systems havingimproved heat transfer capabilities and temperature controls such thatimpurity concentration levels in the purified gas can be reduced and/orsuch that the purified product can have an improved consistency in termsof its product quality.

In another aspect of the invention, the activation time (i.e., which caninclude the time required for the bed to heat up to the desiredactivation temperature, the time for the activation step (includingactivation of a new bed of adsorbent or regeneration of a used bed ofadsorbent) and the time to cool down to operating or ambienttemperature) for adsorbent beds used in such processes and systems canbe reduced.

In accordance with one embodiment of the present invention,semiconductor process fluids (e.g., arsine (AsH₃), phosphine (PH₃) andammonia (NH₃)) can be purified for use by providing at least oneadsorbent vessel having at least one adsorbent bed formed of at leastone adsorbent therein with heat transfer enhancing internals andmaintaining the temperature of the at least one adsorbent bed within apredetermined temperature range while passing the fluid to be purifiedover the at least one adsorbent bed. The adsorbent bed(s) can includeone or more layers of adsorbent(s) (and optionally, one or more layersof thermally conductive layers) and configured such that process fluidflows through the bed(s). The bed(s) can be segmented into sectionsdepending on the configuration of the heat transfer internals (e.g., thenumber and positions of the plate(s)). As a result and as discussedherein, it is expected that the final purified gas product will exhibitimproved consistency in impurity levels and/or improved purity based onthe higher adsorption capacity of adsorbents operating at lowertemperature and narrower temperature ranges.

The present invention more particularly provides purification systemsand methods in which solid plates (which alternatively can beperforated) are in thermal contact with and/or secured to the internalwall of at least one adsorbent vessel such that adequate heat transfercan be accomplished through the wall of the adsorbent vessel from aheating/cooling source external to the adsorbent vessel. Thearrangements provided by the present invention can allow for bothheating and/or cooling of the adsorbent vessel and the at least oneadsorbent bed formed of the at least one adsorbent, with suchheating/cooling being capable of providing more consistent and uniformtemperature distribution and control throughout the adsorbent bed(s). Inaddition, the configurations of the present invention can allow for bothdirect and/or indirect transfer of heat and/or cooling to the adsorbentbed by contacting the adsorbent vessel with one or more heat transferarrangements. For example, direct heating can be provided by immersingthe vessel in a heat transfer fluid. Heat transfer can also be providedby indirect heating, for example by circulating fluid in a heatexchanger in thermal contact with the vessel or by an electrical heatingjacket(s).

Due to more efficient heat transfer within the bed(s), the arrangementsprovided by the present invention allow for flexibility in the selectionof adsorbents to be used during the purification process. Moreover, theconfigurations provided in accordance with the present invention do notrequire heat transfer fluid to flow within the bed, thus reducing oreliminating the potential for contamination of the material beingpurified.

In an embodiment of the present invention, a vessel containing at leastone bed formed of at least one adsorbent therein is provided. At leastone plate in thermal contact with the inner wall of the vessel andformed of material having higher thermal conductivity (e.g., materialsof high thermal conductivity such as aluminum or steel or ceramic) thanthe thermal conductivity of the adsorbent(s) and being inert to the atleast one adsorbent and the process media is used to improve heattransfer to and from the vessel and the bed. The at least one plate maybe solid or perforated and in the case of ceramics, may be porous. Theplates and vessel further improve temperature control within the vesseland bed so that temperature throughout the bed can be maintained withina predetermined temperature range.

The number of plates used in accordance with the present invention canvary, depending on the process and/or system being used, the fluid to bepurified and the characteristics of the adsorbent(s). For example, thenumber of plates can be selected based on a balance between minimizingthe reduction in surface area contact between the fluid being purifiedand the adsorbent(s) and the desired heat transfer parameters of theprocess being utilized. In some embodiments, the number of plates canalso be selected based on limiting the impact of the weight of theplate(s) on the system. In addition, the plate or plates can beconfigured to extend over the entire length and diameter of the bed,while in other embodiments, the plate or plates can extend over aportion of the length and/or diameter of the bed. Determination of thenumber of plates and their configuration can be made based on desiredheat exchange performance and the desired throughput of the material tobe purified. The plates are to be designed to minimize the reduction inthe contact area between the adsorbent(s) and the process fluid balancedwith desired heat transfer characteristics.

In some embodiments of the present invention, thin layers (e.g., layersof beads or perforated wheel(s) of material(s) of high thermalconductivity (e.g., higher thermal conductivity relative to the thermalconductivity of the adsorbent(s))) could be inserted among layers ofadsorption material(s) in the at least one adsorption bed. The thermallyconductive material is to be formed of a material that is chemicallyinert with regard to both the process fluid and impurities as well as tothe adsorbent(s). For example and while not to be construed as limiting,thin layers of aluminum, steel, ceramic materials and/or combinationsthereof could be inserted among layers of adsorption material. In theseembodiments, the configurations are selected to minimize surface areareduction and to maximize contact between the process media (i.e. aprocess fluid such as the fluid being purified and/or an activationfluid such as a purge material) and the adsorbent material to obtainconsistent temperature control within the adsorption bed(s).

In yet other aspects of the present invention (and in addition toimproving the time required for activation), it is expected that thetime to heat and/or cool the adsorption vessel and bed(s) to and fromoperating conditions prior to and following the purification process canbe reduced. More specifically, the adsorption bed(s) can be heated orcooled to a predetermined pre-operating temperature (for example 20° C.)prior to initiating the purification step. During purification, thetemperature of the bed(s) is within a desired operating temperaturerange (for example, within +/−10° C. of about 20° C.) within anacceptable purification temperature range (e.g., −150° C. to 150° C.)based on the adsorption behavior of the material to be purified and theadsorbent type being used. For example and while not to be construed aslimiting, it may be desirable to heat or cool the temperature within thevessel to about 20° C. prior to purification in order to heat or coolthe vessel to operating temperature. The heat transfer arrangements ofthe present invention can be used to more quickly achieve the desiredoperating purification temperature. As discussed herein, it may also bedesirable to heat the vessel and the at least one bed at the end of thepurification step to a predetermined temperature to remove adsorbedfluid prior to disposal of the adsorbent.

During purification and depending on the process being used, the fluidbeing purified and the adsorbent(s) being used, it is usually desirableto maintain the temperature within the bed as uniform as possible withinan acceptable purification temperature range (e.g., −150° C. to 150°C.). For example, it may be desirable to maintain the temperature withinthe bed to within +/−10° C. of the operating temperature (e.g., about20° C.), more preferably within +/−5° C. within the desired operatingtemperature and even more preferably, within +/−3° C. within a desiredoperating temperature. In the past, the temperature within the bed(s)has often risen during purification due to inadequate heat transfercontrol, thereby resulting in less adsorption efficiency and/orinconsistency in product quality. The present invention is expected toovercome such shortcomings by providing for improved heat transferarrangements and controls such that the temperature within the bed(s)during purification is more uniform.

The present invention thus provides methods for purifying gases whichinclude heating or cooling the adsorption vessel, the at least oneadsorption bed(s) formed of the at least one adsorbent therein to apredetermined temperature prior to initiating the purification step suchthat the temperature throughout the bed is within a predeterminedoperating temperature range (for example, within +/−10° C. of a desiredoperating temperature) based on the adsorption behavior of the fluidbeing processed and the adsorbent(s) being used. Feed temperature ofmaterial entering the vessel can be controlled using a heat exchanger orthe like on the feed line. Feed fluid (e.g., gas) to be purified is thenpassed through or over the at least one adsorption bed formed of the atleast one adsorbent under predetermined conditions during thepurification step. During the purification step, cooling (or ifnecessary, heat) can be provided to the at least one adsorption bedformed of the at least one adsorbent to maintain and/or reduce thetemperature within the vessel to a predetermined purificationtemperature range based on the adsorption behavior of the impurity beingremoved. The operating purification temperature will typically be afixed temperature range (e.g., within +/−10° C. of about 20° C.) withina desired acceptable purification temperature range (e.g., from about−150° C. to about 150° C.). During the purification step, thetemperature within the vessel, the bed(s) and the temperature of the gasbeing processed can be monitored and heat transfer (heat and/or cooling)to and from the vessel based on such temperatures can be regulated tomaintain the bed(s) within the desired temperature range.

In an embodiment of the invention, transport of heat to and from theexterior surface of the purifier vessel is expected to involvecontacting the adsorbent vessel with a heat exchanger in the form of oneor more heating/cooling jacket(s) supplied with a suitable heat transferfluid to allow the temperature of the fluid being purified in the vesselto be maintained within the operating purification temperature range.Another alternative embodiment to transport heat to and from theexterior surface of the purifier vessel is expected to involve immersingor partially immersing the vessel in a temperature controlled bath. Inyet other alternative embodiments of the invention, heat transfer to andfrom the vessel is expected to be supplied by one or more electricalheat jacket(s) (which can include cooling capabilities such asflow-through passages for coolant), an oven or other suitable heatexchange method. For example and while not to be construed as limiting,one arrangement for heat transfer to and from the adsorbent bedsincludes conduits located within a shell or jacket(s) made ofmaterial(s) of high thermal conductivity (such as aluminum) which can besecured to the exterior surface of the vessel by clamping or othermeans. Heat transfer fluid having appropriate heat transfer capabilitiesbased on the purification process flows through the shell/jacket(s). Asexplained herein, in some such embodiments, a plurality of jackets canbe utilized to provide more temperature control within the vessel.

Heat transport and control in accordance with the invention is expectedto improve the dynamic adsorption efficiency of adsorption beds, thusproducing purified process fluids having higher purity and/or improvedconsistency in terms of its concentration of impurities and/or producinga higher purity product from the same number of beds.

In addition, the heat transfer controls of the present invention areexpected to allow for operation within a more narrow temperature rangethan in the past. Such operation is less conservative in the sense thatin the absence of such temperature control, the vessel can exhibit moretemperature fluctuation and to maintain product quality, the processtargets often need to be set for the worst case scenario (e.g., the highend of the temperature range). With temperature control in accordancewith the present invention, it is expected that a more precise (e.g.,“aggressive”) target can be set based on narrower temperature range.Consequently, the configurations of the present invention may allowfewer adsorption vessels and/or smaller vessels to be used. Moreover, byoperating the bed at a lower temperature and/or within a narrowertemperature range, it is expected that the useful life of the beds canbe extended beyond current levels. While the relative cost ofimplementing the temperature control system may not be lower than forinstalling multiple vessels in series, it is expected that by allowingfor less conservative operation, fewer vessels will need to bechanged-out than currently practiced. This can be significant because ofthe often highly toxic nature of some materials to be purified and theneed to minimize handling and disposal of such materials.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is made to the following DetailedDescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 shows a jacketed vessel in accordance with an embodiment of thepresent invention;

FIG. 2 a illustrates an alternative embodiment of the present invention;

FIG. 2 b illustrates another alternative embodiment of the presentinvention;

FIG. 3 illustrates yet another embodiment of the present invention;

FIG. 4 shows still another embodiment of the present invention; and

FIG. 5 illustrates yet a further embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As mentioned hereinabove, the present invention relates to methods andsystems for purifying gases, such as for example semiconductor processgases. More specifically, the invention provides gas purificationsystems having improved heat transfer capabilities and temperaturecontrols such that the impurity concentration levels in the purified gascan be reduced and/or such that the purified product can have animproved consistency in terms of its product quality.

In another aspect of the invention, the activation time (i.e., which caninclude the time required for the bed to heat up to the desiredactivation temperature, the time for the activation step (includingactivation of a new bed of adsorbent or regeneration of a used bed ofadsorbent) and the time to cool down to operating or ambienttemperature) for adsorbent beds used in such processes and systems canbe reduced.

In accordance with one embodiment of the present invention,semiconductor process gases (e.g., arsine (AsH₃), phosphine (PH₃) andammonia (NH₃)) can be purified by providing at least one adsorbentvessel containing at least one adsorbent bed formed of at least oneadsorbent(s). The vessel further contains heat transfer internals andcontrols for maintaining the temperature within the vessel at anoperating temperature range (e.g., within +/−10° C. within about 20° C.)within an acceptable purification temperature range (e.g., −150° C. to150° C.). As a result, it is expected that the final purified gasproduct will contain reduced impurity levels relative to the prior artand/or will exhibit improved product consistency due to improvedtemperature control within the bed(s).

In addition, the present invention is expected to provide economicadvantages in that it can be easily integrated into existing gaspurification systems. This ease of integration is based on an ability toaccommodate heat transfer using a variety of different methods,involving either direct or indirect heat transfer capabilities. Anotheradvantage of the present invention is the flexibility to select theadsorbent material(s) that best suits the specific purification process.The present invention can further avoid potential contamination risks byavoiding heat transfer fluid flow within the adsorbent bed(s).

Referring now to FIG. 1, an embodiment of the present invention isillustrated. In this embodiment, vessel 10 includes at least oneadsorption bed formed of at least one adsorbent 24 therein. Theadsorbent bed(s) can include one or more layers of adsorbent(s) (andoptionally, one or more layers of thermally conductive layers) andconfigured such that process fluid 20 flows through the bed(s). The bedcan be segmented into sections depending on the configuration of theheat transfer internals (e.g., the number and positions of theplate(s)).

Vessel 10 can be constructed from any material having sufficiently highthermal conductivity to transfer heat/cooling to and from the externalheat source and the adsorbent bed(s), plate(s) and thermally conductivelayer(s) (if present). For example and while not to be construed aslimiting, metals such as steel, (e.g., stainless steel, carbon steel orthe like), aluminum, nickel, copper or ceramics and combinations thereofmay be suitable material(s) for construction of vessel 10 in accordancewith the present invention. It will be appreciated by those skilled inthe art that the thermal conductivity of the vessel should be greaterthan the thermal conductivity of the adsorbent(s). It will also beappreciated that the material(s) of construction of vessel 10 should beinert with respect to the process media (i.e. a process fluid such asthe fluid being purified and/or an activation fluid such as a purgematerial).

Vessel 10 has a radius R_(vessel) and the bed has a radius R_(bed) inwhich R_(vessel) is equal to R_(bed). Vessel 10 also has a lengthL_(vessel) while the bed has a length L_(bed). In preferred embodiments,L_(bed) is equal to L_(vessel).

The at least one adsorbent bed formed of the at least one adsorbent canbe positioned in vessel 10 in a variety of configurations. For exampleand while not to be construed as limiting, at least one adsorbent can bepositioned in one or more layers (including layers of physical mixturesand/or composites) in vessel 10 and can be formed of more than oneadsorbent material. As discussed hereinabove, the arrangements of thepresent invention allow flexibility in selecting the desiredadsorbent(s) for the gas being purified.

At least one plate 12 having a width W_(plate) and a length L_(plate) isin thermal contact with the inner wall 10 a of vessel 10. The at leastone plate(s) 12 can be solid or perforated. In some embodiments, thenumber of plates will be greater than two. In such embodiments, all ofthe plates may be solid, all of the plates may be perforated or some ofthe plates may be solid and some may be perforated. The plate(s) 12 areto be formed of material having higher thermal conductivity than thethermal conductivity of the adsorbent(s) to improve heat transfer to andfrom vessel 10. The material(s) of construction of plate(s) 12 shouldalso be inert with respect to the process media (i.e. a process fluidsuch as the fluid being purified and/or an activation fluid such as apurge material) and the adsorbent(s).

The number of plates will be at least one and are to be designed tominimize the reduction in the contact area between the at least oneadsorbent and the process media. More specifically, the number of platescan be selected based on a balance between minimizing the reduction insurface area contact between the process media and the adsorbent(s) anddesired heat transfer parameters of the process being utilized. In someembodiments, the lengths of the plates may not all be equal. As furthershown in FIG. 1, the plates can extend the entire length of the vesselL_(vessel) and have a radius of the bed R_(bed) such thatW_(plate)=R_(bed)=R_(vessel). The number of plates shown in FIG. 1 isfour and is intended to be for purposes of illustration and is not to beconstrued as limiting. Alternatively, W_(plate) can be less than theinternal radius of the vessel R_(vessel) (shown in FIG. 2 a) or can haveW_(plate) greater than R_(vessel), but less than or equal to theinternal diameter of the vessel (see for example FIG. 2 b).

Preferred materials of construction of the plate(s) include materialssuch as metals, ceramics, thermally conductive plastics and combinationsthereof. Exemplary metals include, but are not limited to, aluminum,steel, nickel, copper, tantalum, gold, and metal alloys. The selectedmaterial(s) do not readily react with the process media (i.e. a processfluid such as the fluid being purified and/or an activation fluid suchas a purge material) or adsorbent(s). Other materials could be used forthe plate construction as long as the material(s) is inert with regardto the process media and adsorbent material(s) and has sufficiently highthermal conductivity as described hereinabove. The material(s) ofconstruction for the at least one plate(s) 12 could be the same ordifferent from the material(s) of construction for the vessel. Dependingon the process, the at least one plate(s) 12 may thus be of higherthermal conductivity than the vessel or vice versa. Alternate materialsof construction of the plates for example could include any metals orceramics or combinations thereof that offer sufficient thermalconductivity for the given application and do not readily react with theprocess media (i.e. fluid being purified and/or purge material) oradsorbent(s). In some embodiments, the plates will be perforated toallow for increased contact between the adsorbent(s) and the processmedia. In cases where the plates are constructed of ceramics or othernon-metal materials (e.g., thermally conductive plastic), the plates mayalso be porous.

The thickness of the plate(s) is to be selected such that heating and/orcooling can be transferred to the adsorbent bed(s) to maintain thebed(s) within a predetermined temperature range during both activationof the bed as well as during the gas purification process (includingheating and/or cooling prior to and after purification). In someembodiments where weight of the equipment is an issue, the thickness ofthe plate(s) and the material of construction can also be selected tolimit the overall impact on the weight of the vessel. The plates andheat transfer source improve temperature control within the vessel sothat temperature uniformity throughout the bed(s) is improved.

As mentioned above, the at least one plate(s) 12 is in thermal contactwith inner wall 10 a of vessel 10 such that heat transfer can occur toand from inner wall 10 a and plate(s) 12. In some embodiments, plate(s)12 can also be secured to inner wall 10 a by any of several methods. Forexample and while not to be construed as limiting, plate(s) 12 can besecured to wall 10 a by: welding, soldering, nuts and bolts, adhesive,inserting plate(s) 12 into grooves formed in inner wall 10 a and thelike. In some embodiments, a plurality of solid and/or perforated platescould be arranged together with a central axis to form a thermallyconductive integrated unit. The thermally conductive unit could then beinserted into the vessel 10. Such embodiments may be suitable forretrofit applications. Adsorbent(s) could then be loaded in the vessel10 for the desired process.

In some illustrative embodiments of the invention, a plurality ofperforated plates 12 in thermal contact (e.g. by welding or the like)with the inner wall 10 a of the adsorption vessel 10 can be used. Theplates can extend over the entire length of the vessel or bed such thatheat transfer occurs along the length of the vessel or bed respectively.The plates can also extend beyond the length of the bed when the lengthof the bed is less than the length of the vessel. In such embodiments,the lengths of the plates are confined by the length of the vessel. Inother embodiments of the invention, the length of the bed, length of thevessel and length(s) of some or all of the plates are all equal. Thewidth of the plates can be equivalent to the internal radius of thevessel (W_(plate)=R_(vessel)) In this manner, heat transfer can extendover the entire length and width of the bed.

As further mentioned above, the number of plates is at least one and canvary in number. The plate or plates can be configured to extend over theentire length and diameter of the bed, while in other embodiments, theplate or plates extend over a portion of the length and/or diameter ofthe bed. In some cases and particularly where there may be a safetyfactor between theoretical loading capacity and actual loading allowedin the field, it may be preferred not to have the plate(s) extend thelength of the bed or vessel because adsorption may not occur in someregions of the bed or vessel. As mentioned above, the plates are to bedesigned to minimize the reduction in the contact area between theadsorbent bed and the process media considered with the desired heattransfer characteristics.

The at least one adsorbent in the bed could be any adsorbent orcombination of adsorbents selected for the particular application (i.e.the fluid to be purified). The adsorbent or adsorbents could likewise beprovided in one or more layers and further include layers of inertmaterials (e.g., pellets, balls or the like) above and/or below theadsorbent layer(s). For example and while not to be construed aslimiting, the adsorbent or adsorbents could include activated carbon,alumina, silica and zeolite molecular sieves such as for example 3A, 4A,5A, 13X and combinations thereof. The present invention, however, is notlimited to the use of such adsorbent(s). Depending on the application,other adsorbents may be suitable for use in accordance with the presentinvention.

As further illustrated in FIG. 1, transport of heat to and from theexterior surface of the adsorbent vessel 10 can include contacting, forexample by surrounding the adsorbent vessel, with a heat exchanger inthe form of a heating/cooling jacket supplied with a suitablecirculating heat transfer fluid 18 to allow the temperature of the fluidbeing purified to be maintained within a purification temperature range,for example between about −150° C. and 150° C. For example, it isusually desirable to maintain an adsorption temperature distributionprofile within a vessel and adsorption bed as uniform as possible duringa purification process. For purposes of illustration, if a purificationis being performed at ambient temperature (e.g., 20° C.), it is usuallypreferred to maintain the temperature throughout the vessel 10 and theat least one adsorption bed within +/−10° C. of about 20° C., morepreferably within +/−5° C. of about 20° C. and still more preferablywithin +/−3° C. of about 20° C. The precision of the range within theacceptable operating temperature range (e.g., −150° C. to 150° C.) canbe selected based on the cost of the heat transfer system, the cost torun the heat transfer system, the desired product purity, the desiredproduct consistency and the like. In accordance with the presentinvention, heat transfer (heating and/or cooling) to the vessel (andhence to the at least one bed formed of the at least one adsorbent)could therefore occur through use of a heating jacket or through use ofa heating fluid either flowing through a jacket or directly in contactwith the surface of vessel 10. In some embodiments, the heat transfersystem may surround the vessel, while in other embodiments it may not bedesirable or preferred for the heat transfer system to surround thevessel. In either case, the heat transfer system is positioned to be inthermal contact with the vessel and provide the appropriate heatingand/or cooling to the vessel.

More specifically, heat transfer to and from adsorbent vessel 10 shownin FIG. 1 by arrows 14 can be accomplished using a heat exchanger 16 andcirculating fluid 18. Thermocouples T₁ to T_(n) located in the bed andin the process media piping could be used to monitor and regulate thetemperature of the bed(s) within vessel 10 as well as the incomingtemperature T1 of the process fluid 20 (i.e. the fluid to be purified)and the temperature Tn of product gas 22. The number and location ofthermocouples used in the bed and within the process piping is optionaland can be selected based on the particular process being utilized andthe fluid being processed. Additionally, the feed temperature of the gasto be purified can be controlled using methods known to those skilled inthe art, such as through the use of a heat exchanger on the feed line20. As discussed herein, other external heat transfer arrangements canbe used in accordance with the present invention.

In other alternative embodiments of the present invention, theL_(plates) can be greater than the L_(bed) and configured such that theplate(s) can provide heat to the process fluid 20 entering vessel 10.The adsorbent(s) 24 is positioned downstream of such heat source in amanner that the adsorbent bed(s) is positioned proximate to the productend of vessel 10 for product gas 22.

Vessels in accordance with the present invention can be manufactured andthe appropriate internals (including plate(s), thermocouples and thelike) can be positioned in the vessel. Adsorbent(s) can then be loadedinto the vessel. The bed(s) in the loaded vessel can be activated usingone of the heat transfer arrangements. Thereafter, the vessel can bemoved to another location or remain in the same location and the same ora different heat transfer arrangement can be used for the purificationprocess.

Referring now to FIG. 2 a, an alternative embodiment in accordance withthe present invention is illustrated (adsorbent(s) not shown in FIG. 2a). The number of plates shown in FIG. 2 a is seven (three in front andfour in the back of the figure) and is intended to be for purposes ofillustration and is not to be construed as limiting. In this embodiment,plates can extend over any portion of the entire length of the vessel(L_(plate)≦L_(vessel)) and have a width equivalent to some portion ofthe internal radius of the vessel (W_(plate)≦R_(vessel)). The number ofheat transfer plate(s) 12 in such embodiment is at least one and canvary depending on the process and process media. In one particular andexemplary arrangement shown in FIG. 2 a, the L_(plate) is equal toL_(vessel), but the width of each plate (W_(plate)) is less than theR_(vessel). The plates can be arranged at various angles relative to theentrance and exit of the vessel 10 corresponding to the cocurrent and/orcountercurrent direction of flow of the process media. In preferredembodiments, however, the plates are arranged substantially parallel tothe cocurrent and/or countercurrent direction of flow of the processmedia. As also shown in FIG. 2 a, heat transfer to and from vessel 10 issimilar to that shown in FIG. 1. Alternatively, heat transfer to andfrom vessel 10 could be accomplished in accordance with any of the otherarrangements discussed herein.

FIG. 2 b illustrates another embodiment in accordance with the presentinvention (adsorbent(s) not shown in FIG. 2 b). The number of platesshown in FIG. 2 b is three and is intended to be for purposes ofillustration and is not to be construed as limiting. In this embodiment,plates can extend over any portion of the entire length of the vessel(L_(plate)≦L_(vessel)) and have a width equivalent to less than or equalto the diameter of the vessel, D_(vessel) (W_(plate)≦D_(vessel)). Thenumber of heat transfer plate(s) 12 in such embodiment is at least oneand can vary depending on the process and the process media. In oneparticular and exemplary arrangement shown in FIG. 2 b, the L_(plate) isequal to L_(vessel), but the width of each plate (W_(plate)) is greaterthan the internal radius of the R_(vessel). The plates can be arrangedat various angle(s) relative to the entrance and exit of the vessel 10corresponding to the cocurrent and/or countercurrent direction of flowof the process media. In preferred embodiments, however, the plates arearranged substantially parallel to the cocurrent and/or countercurrentdirection of flow of the process media. As also shown in FIG. 2 b, heattransfer to and from vessel 10 is similar to that shown in FIG. 1.Alternatively, heat transfer to and from vessel 10 could be accomplishedin accordance with any of the other arrangements discussed herein.

FIG. 3 illustrates yet another embodiment of the present invention. Theembodiment shown in FIG. 3 includes one or more high thermallyconductive layer(s) 26 positioned between one or more adsorbent layer(s)24. Thermally conductive layer(s) 26 may be formed of thermallyconductive perforated wheels, one or more layer(s) of thermallyconductive beads, and/or combinations thereof. The inclusion of layer(s)26 can be used to further improve the heat transfer capabilities andcontrols to and from the vessel and within the vessel. Layer(s) 26 is tobe formed of material having higher thermal conductivity (e.g.,materials of high thermal conductivity such as aluminum, steel, nickel,copper, tantalum, gold, ceramic or combinations thereof) than thethermal conductivity of the adsorbent(s) and is to be inert with respectto the at least one adsorbent and the process media. The material(s) ofconstruction for layer(s) 26 could be the same or different from thematerial(s) of construction for the at least one plate. Depending on theprocess, layer(s) 26 may thus be of higher thermal conductivity than theplate(s) or vice versa. The material(s) of construction for layer(s) 26could also be the same or different from the material(s) of constructionfor the vessel. Depending on the process, layer(s) 26 may thus be ofhigher thermal conductivity than the vessel or vice versa.

FIG. 4 shows another embodiment of the present invention in which anelectrical heating jacket 28 is utilized to provide heat transfer to andfrom vessel 10 (adsorbent(s) not shown in FIG. 4). More specifically,electrical heating jacket 28 is in thermal contact with vessel 10 and isconfigured to provide heat to vessel 10. In some embodiments, electricalheating jacket 28 is also configured to provide cooling (e.g. throughthe use of a flow through jacket or the like).

In other alternative embodiments in which there is an electrical heatsource (such as in FIG. 4) or circulating heat transfer fluid in ajacket (such as in FIG. 1), it is expected that independent temperaturecontrol of one or more regions corresponding to one or more designatedthermocouples can be accomplished through the use of multiple heatjackets. Each heat jacket could thus have separate inlets and outletsfor transferring heat to and from the respective regions in response tofeedback from the corresponding thermocouples.

In still other alternative arrangements, heat could be transferred toand from adsorbent vessel 10 by immersing or partially immersing vessel10 in a temperature controlled bath or by supplying heat or coolingusing an oven or other suitable heat exchange method. For example andwith reference to FIG. 5 (adsorbent(s) not shown in FIG. 5), heattransfer to and from vessel 10 can be accomplished by partiallyimmersing vessel 10 in temperature controlled bath 30. The temperatureof the bath 30 can be controlled by controlling the temperature of thebath fluid 32 by appropriate methods. Bath fluid 32 may be any fluidsuitable for providing adequate heating and/or cooling to vessel 10. Inthe embodiment shown in FIG. 5, it will be understood that heating andcooling would not be used simultaneously. Bath fluid 32, however, may beused for both heating and cooling by changing the temperature of thefluid in the bath. Alternatively, the bath fluid 32 may include a fluidfor heating during activation and thereafter, the fluid may be changedto a coolant for use during purification. More specifically, vessel 10could be immersed or partially immersed in a bath 30 containing anappropriate heat transfer fluid. Thereafter, bath 30 could be drainedand fluid 32 replaced with another suitable fluid for the intendedprocess. In still other embodiments, vessel 10 could be removed andplaced in another bath 30 containing a coolant for the purificationprocess. Exemplary heating fluids and/or coolants may include water,liquid nitrogen, glycol or other suitable heat transfer fluid. Thesecoolants and heating fluids are illustrative and not to be construed aslimiting. Other coolants and heating fluids capable of providing thedesired cooling or heating capabilities to vessel 10 for a given processmay be used in accordance with the present invention. Those skilled inthe art will be able to select an appropriate heat transfer fluid(s).

In other aspects of the present invention, it is expected that theactivation time (i.e., which can include the time required for the bedto heat up to the desired activation temperature, the time for theactivation step (including activation of a new bed of adsorbent orregeneration of a used bed of adsorbent) and the time to cool down toprocess or ambient temperature) for adsorbent vessels beds used in suchprocesses and systems can be reduced. During activation of the bed andprior to initiating a purification process, dry purge gas can be passedthrough the vessel and over the at least one adsorbent bed and at leastone adsorbent in a direction cocurrent or countercurrent to the flow ofgas to be purified such that adsorbed species on the adsorbent(s) can beremoved. In preferred embodiments, the flow of the purge gas is in adirection countercurrent to the direction of flow of the gas to bepurified and purge gas containing desorbed compounds exits the end ofthe bed opposite the feed end of the purge gas.

Various purge gases can be used in accordance with the present inventionso long as the purge gas is inert with respect to the adsorbent(s) inthe bed and the fluid to be purified. For example and while not to beconstrued as limiting, nitrogen, hydrogen, helium, or argon can be usedas purge gas, alone or in sequence with one another. In accordance withthe present invention, it is expected that the time required foractivation prior to use in the purification process or in a regenerationmode of the adsorbent(s) when the adsorbent(s) is to be reused can bereduced due to the improved heat transfer controls provided herein.

For purposes of illustration and while not intending to be bound by aspecific method of activation, an exemplary activation process couldinclude the following. Following loading of the adsorbent in a vesselhaving the desired heat transfer internals of the present inventiontherein, an activation step to remove moisture (and/or other impurities)can be provided by using one or more inert purge gases such as nitrogen.More specifically, nitrogen can be introduced into the vessel and passedthrough the vessel in a countercurrent mode to raise the temperaturewithin the vessel to a predetermined temperature (e.g., 300° C.). Thetemperature within the vessel is maintained for a period of time (e.g.,about 60 hours). The heat transfer source to the vessel can then beturned off and the vessel allowed to cool. In some embodiments, nitrogenmay be used and passed through the vessel during all three steps ofactivation (heating the vessel, maintaining the temperature of thevessel and cooling the vessel). The nitrogen and any desorbed componentscan be removed at the inlet 20 of vessel 10. For some processes, it maybe desirable to change the activation fluid (e.g., purge gas such asnitrogen) to a second activation fluid (e.g., purge gas such as helium)for use during a part of the activation step and cooling step. Similarsteps can be used for regeneration of the at least one adsorbent when itis desirable or preferable to do so. The heat transfer arrangements ofthe present invention can be used to reduce the time required for any orall of the three steps of such activation.

Referring again to FIG. 1, in a preferred embodiment of the invention,dry purge gas could flow down through adsorbent vessel 10 duringactivation of the bed(s) and purge gas containing desorbed compoundswould leave through the inlet to the vessel. Addition of heat to the bedcould occur through use of a heating jacket or other heat transfersources discussed hereinabove. Thermocouples T₁ to T_(n) located in thevessel and in the purge gas piping could be used to control addition orremoval of heat via the heating jacket. During activation of the bed,the temperature of the bed and adsorbent(s) are raised to a temperatureof between about 100-400° C. (e.g., 350° C. to remove moisture). Suchtemperature range can vary, however, depending on the adsorbent(s) usedand the fluid being purified.

During purification, the process fluid 20 preferably enters vessel 10 atthe opposite end from the purge gas and the purified product exitsvessel 10 as product 22. Feed temperature of gas entering the vessel canbe controlled using a heat exchanger or the like on the feed line. Feedgas to be purified is then passed through vessel 10 and over the atleast one adsorption bed formed of the at least one adsorbent underpredetermined conditions during a purification step. During thepurification step, heating and/or cooling can be provided to theadsorption bed to maintain and/or reduce the temperature within the bedto an operating temperature range (e.g., within +/−10° C. of 20° C.)within an acceptable purification temperature range (e.g., −150° C. to150° C.). During the purification step, the temperature within the bedand the temperature of the gas being processed are monitored and heattransfer to and from the bed based on temperature are regulated tomaintain the bed within the desired temperature range. The vessel can beheated and/or cooled through flow of a heat transfer fluid (e.g.,heating fluid and/or coolant 18) through a jacket, by immersing orpartially immersing the bed in a coolant or through any of the methodsdescribed hereinabove.

Following purification, the process may include a decontamination stepin which nitrogen or another inert gas is fed through the vessel toremove or desorb process fluid such as arsine or phosphine which hasbeen adsorbed on the adsorbent(s). Given the toxicity of some processfluids, such decontamination steps are sometimes included prior todisposal of the adsorbent even when the adsorbent(s) is not to bereused. The present invention can be used during such decontaminationstep to better control the heat transfer to and from the vessel and thetemperature within the vessel during decontamination.

The present invention allows for further flexibility in selectingdesirable heat transfer systems by providing vessels that can beactivated in situ or in locations other than the purification site. Forexample, vessels in accordance with the present invention can bemanufactured and the appropriate internals (including plate(s),thermocouples and the like) positioned in the vessel. Adsorbent(s) canthen be loaded into the vessel. The bed(s) in the loaded vessel can beactivated using one of the heat transfer arrangements discussed above.Thereafter, the vessel can be moved to another location or remain in thesame location and the same or a different heat transfer arrangement canbe used for the purification process. This increases the ability toselect various heat transfer options and heat transfer fluids for agiven process.

As discussed hereinabove, the present invention allows gases such assemiconductor process gases (e.g., arsine, phosphine and ammonia) to bepurified. The present invention, however, can also be used with othergases to be purified. The present invention could be used with otheradsorption processes than purification of semiconductor gases. Forexample and while not to be construed as limiting, the present inventioncould be used in adsorption applications such as pressure swingadsorption (PSA) processes, vacuum pressure swing adsorption (VPSA)processes, temperature swing adsorption (TSA) processes and combinationsthereof. In addition, the present invention is expected to be suitablefor use in the adsorption aspects of U.S. Pat. No. 6,576,138 B2. Thepresent invention is expected to be applicable to fluids to be purified.It is understood that such fluids can be in a liquid or gaseous state.

The present invention thus provides for direct or indirect heatingand/or cooling. This is expected to improve the dynamic adsorptionefficiency of the adsorption bed, thus requiring potentially fewer bedsto be used and/or producing a higher purity product from the same numberof beds. Additionally, by operating the bed within a narrow temperaturerange (i.e. a less conservative mode of operation), it may be possibleto extend the useful life of the bed(s) beyond current levels. While therelative cost of the temperature control system may not be lower thanfor multiple beds in series, the potential to change-out fewer beds thanpracticed today is significant because of the often highly toxic natureof the materials being purified and the need to minimize handling anddisposal of these materials.

It should be appreciated by those skilled in the art that the specificembodiments disclosed above may be readily utilized as a basis formodifying or designing other structures or methods for carrying out thesame purposes of the present invention. It should also be realized bythose skilled in the art that such equivalent constructions do notdepart from the spirit and scope of the invention as set forth in theappended claims.

1. An adsorbent vessel having an inner surface and an outer surface, thevessel comprising: at least one adsorbent bed formed of at least oneadsorbent; at least one plate in thermal contact with the inner surfaceof the vessel and formed of material having higher thermal conductivitythan the thermal conductivity of the at least one adsorbent; an externalheat exchanger in contact with the outer surface of the vessel tomaintain a fluid being purified within an operating purificationtemperature range; and wherein the at least one plate is configured totransfer heat and/or cooling to and from the at least one adsorbent bed.2. The adsorbent vessel of claim 1, wherein the at least one plate isformed of a solid material.
 3. The adsorbent vessel of claim 2, whereinthe at least one plate is foiled of material selected from the groupconsisting of: metals, ceramics, thermally conductive plastics andcombinations thereof.
 4. The adsorbent vessel of claim 3, wherein themetal is selected from the group consisting of: aluminum, steel, nickel,gold, tantalum and metal alloys.
 5. The adsorbent vessel of claim 1,wherein the at least one plate is perforated.
 6. The adsorbent vessel ofclaim 5, wherein the at least one plate is formed of material selectedfrom the group consisting of: metals, ceramics, thermally conductiveplastics and combinations thereof.
 7. The adsorbent vessel of claim 6,wherein the metal is selected from the group consisting of: aluminum,steel, nickel, gold, tantalum and metal alloys.
 8. The adsorbent vesselof claim 1, wherein the at least one plate is secured to the inner wallof the vessel.
 9. The adsorbent vessel of claim 8, wherein the at leastone plate is welded to the inner surface of the vessel.
 10. Theadsorbent vessel of claim 1, wherein the number of plates is greaterthan
 2. 11. The adsorbent vessel of claim 1, further including means tomonitor temperature inside the vessel.
 12. The adsorbent vessel of claim11, wherein the means to monitor temperature comprises at least onethermocouple.
 13. The adsorbent vessel of claim 1, wherein the externalheat exchanger comprises an electrical jacket.
 14. The adsorbent vesselof claim 1, wherein the external heat exchanger comprises a heattransfer fluid configured to transfer heat to and from the vessel. 15.The adsorbent vessel of claim 14, wherein the external heat exchangercomprises a circulating heat transfer fluid.
 16. The adsorbent vessel ofclaim 14, wherein the external heat exchanger comprises a bath for atleast partially immersing the vessel therein.
 17. The adsorbent vesselof claim 1, wherein the at least one plate has a width less than theradius of the vessel.
 18. The adsorbent vessel of claim 1, wherein theat least one plate has a width less than the diameter of the vessel. 19.The adsorbent vessel of claim 1, wherein the at least one plate has alength equal to a length of the at least one adsorbent vessel.
 20. Theadsorbent vessel of claim 19, wherein the number of plates is greaterthan two.
 21. The adsorbent vessel of claim 19, wherein the at least oneplate has a width less than a radius of the adsorbent vessel.
 22. Theadsorbent vessel of claim 21, wherein the at least one adsorbent bed hasa radius equal to the radius of the adsorbent vessel.
 23. The adsorbentvessel of claim 22, wherein the number of plates is greater than two.24. The adsorbent vessel of claim 19, wherein the at least one plate hasa width equal to a radius of the adsorbent vessel.
 25. The adsorbentvessel of claim 24, wherein the at least one adsorbent bed has a radiusequal to the radius of the adsorbent vessel and the width of the atleast one plate.
 26. The adsorbent vessel of claim 25, wherein thenumber of plates is greater than two.
 27. The adsorbent vessel of claim19, wherein the at least one plate has a width greater than a radius ofthe adsorbent vessel.
 28. The adsorbent vessel of claim 27, wherein theat least one adsorbent bed has a radius equal to the radius of theadsorbent vessel.
 29. The adsorbent vessel of claim 27, wherein thenumber of plates is greater than two.
 30. The adsorbent vessel of claim19, wherein the at least one plate has a length equal to a length of theat least one adsorption bed and a length of the adsorbent vessel. 31.The adsorbent vessel of claim 1, wherein the at least one plate has alength greater than the at least one adsorption bed and less than alength of the adsorbent vessel.
 32. The adsorbent vessel of claim 1,wherein the vessel is formed of aluminum, steel, ceramic material orcombinations thereof.
 33. The adsorbent vessel of claim 30, wherein thevessel is formed of stainless steel.
 34. The adsorbent vessel of claim1, further including at least one thermally conductive layer positionedin the adsorbent vessel such that during operation process media flowsthrough the at least one adsorbent bed and the at least one thermallyconductive layer.
 35. The adsorbent vessel of claim 34, wherein the atleast one thermally conductive layer is formed of one or more materialscomprising metals, ceramics, thermally conductive plastics orcombinations thereof.